The present invention relates to a chuck unit for a power hand tool, and more particularly to such a chuck unit which can be manually or automatically operated to hold down/release the inserted bit and, which keeps the bit to be rotated stably.
FIG. 1 shows a T-shaped spanner used with a conventional power hand drill. The bit chuck of this structure of power hand drill is driven to hold down/release the bit by hand with the T-shaped spanner. Because the bit chuck of this structure of power hand must be driven to hold down/release the bit by hand with the T-shaped spanner, the power hand tool becomes unable to be operated if the T-shaped spanner is missed. FIGS. 2 and 3 show another arrangement of chuck unit for a power hand tool according to the prior art. This structure of chuck unit comprises a barrel having three equiangularly spaced oblique guide holes, three threaded clamping rods respectively inserted into the oblique guide holes, a nut threaded onto the threaded clamping rods and rotated with a front cover shell to move the clamping rods between the clamping position and the relief position.